Cellulosic photoconductive imaging member containing carboxyl reactive groups



United States Patent 3,486,889 CELLULOSIC PHOTOCONDUCTIVE IMAGING MEMBERCONTAINING CARBOXYL REAC- TIVE GROUPS Edward G. Bobalek and John R.Hart, Orono, Maine, and Donald L. Fauser, Cleveland, Ohio, assignors toHarris-Intertype Corporation, Cleveland, Ohio, a corporation of DelawareNo Drawing. Filed Feb. 7, 1966, Ser. No. 525,294 Int. Cl. G03g 7/00 US.Cl. 96--1.8 23 Claims ABSTRACT OF THE DISCLOSURE A photconductiveimaging member is composed of matted and intertwined fibers containingcarboxyl reactive groups which are capable of chemically associatingtherewith a metal ion containing photoconductor, the resulting memberbeing in the form of a flexible self-supporting sheet. The imagingmember is free of mobile ionic charge carriers thus providing a surfaceportion of high electrical resistance in the dark. The fibers may becellulosic containing materials such as wood pulp, cotton or othernaturally occurring cellulose containing fiber materials. The content ofreactive carboxyl groups in the fiber may be increased over thatoccurring naturally by (1) bleaching chemically pure pulp, (2) an ionexchange reaction in which ferrous ions are exchanged with carboxylgroups followed by reacting acrylic acid near the site of the exchangereaction, and (3) admixing a latex of a carboxylated polymer with thefibrous furnish.

This invention relates to an improved photoconductive imaging membercomprised of a photoconductive material and a multiplicity of fibers,the fibers containing reactive groups capable of chemically associatinga photoconductor material thereto, the fibers being formed into aself-supporting sheet containing a sufficient amount of substantiallypermanently associated photoconductor material to provide aphotoconductive imaging member.

Imaging members for electrostatic photography are known which include abase having a surface coating thereon which includes photoconductivematerial dispersed in a binder which acts to bind the particles to eachother and to the base. These binders are usually synthetic or naturalresins or polymers which provide an electrically insulating mediumholding the photconductor in place on the base. A variety of bases havebeen utilized including metal or metal foils, paper and electricallyconductive plastic sheet material. In each case, the photoconductivesurface layer is formed on the base by a coating operation performedafter formation of the base.

In the case of an imaging member comprising a coating on a paper base,the paper base is formed by conventional paper making techniques and asis usual, the paper base itself includes what is referred to as a wireside and a felt side. The two different sides of the sheet havedifferent characteristics, the felt side being much smoother, and theusual practice is to coat the photoconductivebinder layer on the feltside of the sheet. Sometimes, the practice includes the use of a sizecoating over either the wire side or felt side of the sheet in order toprovide a smooth base surface upon which the photoconductive layer isdeposited, and in some instances, this intermediate layer is used toprovide an electrically conductive layer intermediate the paper base andthe photoconductive coating. This intermediate layer may also functionas a barrier layer to prevent cross-migration of components from thepaper to the photoconductive layer.

The ratio by weight of photoconductor to binder in 3,486,889 PatentedDec. 30, 1969 ice imaging members of the type above described variesfrom 1:1 to 25:1, and the photoconductor commonly used isphotoconductive zinc oxide prepared by the French process, a processwill known in electrophotography. The resultant coated paper sheetusually has a relatively high basis weight as compared to ordinarycoated papers and has a significant portion of the weight in thephotoconductive layer. Another characteristic of coated paper imagingmembers utilizing a relatively high proportion of photoconductive zincoxide pigment in the coating is the somewhat abrasive nature of thecoated sheet. Other photoconductor pigments used in a coated sheet, suchas photoconductive titanium dioxide and zinc sulphide, also exhibitsimilar abrasive characteristics.

The resin component and dispersed photoconductor of the coated imagingmember may be deposited from an organic solvent, from an aqueous medium,or by hot melt technique. The usual procedure is to prepare a coatingmixture which is deposited on a web of the base material by conventionalpaper converting equipment such as an air knife coater, reverse rollcoater, trailing blade coater and the like.

In the event that a photoconductive layer is desired on each side of thebase, two coating operations are required and care must be taken in thesecond coating operation not to affect adversely the coating previouslyformed on the reverse side of the base.

In accordance with the present invention the use of a binder or adhesivecontaining dispersed photoconductor to form a separate layer on a baseis eliminated. Instead, a sufficient amount of photoconductive materialis substantially permanently chemically associated with the fibrousmaterial of a self-supporting sheet to provide a photoconductive imagingmember. The chemical association in accordance with the presentinvention is believed to be in the nature of an ionic bond between areactive site on or bonded to the fiber and the surface of theparticulate photoconductor, or by chemi-sorption, or a combination ofboth types of bonding, and is to be distinguished from mere mechanicaltrapping of the photoconductor by the matted fibrous material.

Formation of an image member of the type in accordance with the presentinvention offers several advantages, the first of which is that in thecase of cellulose containing fiber materials such as wood fiber, thesheet may be formed by adding the photoconductor to the aqueous pulpslurry, and forming the resultant imaging member during the felting ofthe fibers which takes place on the paper making machine. Anon-two-sided paper, that is, a sheet having surfaces of substantiallythe same physical characteristics on each side, may be provided by useof a vertical paper forming machine such as a Verti-Forma machine,details of which are shown in US. Patents 2,969,- 114 and Re. 25,333.

Accordingly, it is a primary object of the present invention to providea self-supporting imaging member having high electrical resistance inthe dark and including photoconductive material and a multiplicity offibers, at least a portion of the photoconductive material beingsubstantially permanently chemically associated with the fibers of themember.

Another obiect of the present invention is the provision of alight-weight electrophotoconductive fiber-containing sheet including aparticulate photoconductor at least a portion of which is substantiallypermanently chemically associated directly to the fibers of the sheet.

Another object of the present invention is the provision of an imagingmember as described above wherein the fibrous material containscellulose.

Another object of the present invention is the provision ofelectrophotographic imaging members comprised of fibrous materialcontaining reactive groups wherein these groups are naturally present orchemically reacted into or on the fiber structure and wherein the fibersare formed into a self-supporting sheet, the reactive groups of thefiber operating to provide substantially permanent chemical associationof a photoconductor into the sheet structure.

Another object of the present invention is the provision of an imagingmember as above described wherein the reactive groups are carboxylgroups.

Another object of the present invention is the provision of anelectrophotographic imaging member comprised of photoconductivematerial, fibrous material and a polymer, each of the latter containingreactive groups, the photoconductor being capable of chemicallyassociating with the respective reactive groups, and the reactive groupspreferably being carboxyl groups.

Another object of the present invention is the provision of anelectrophotographic imaging member at least one outer surface portion ofwhich comprises a photoconductor substantially permanently chemicallyassociated to a network of cellulose fibers by reactive groupsassociated with the fibers.

Another object is the provision of an electrophotographic imaging memberincluding a particulate photo conductor wherein the performance of theimaging member in uses other than for electrophotography is similar toconventional uncoated paper, and which may be manufactured usingconventional paper making machinery.

A further object of the present invention is the provision of methodsfor forming electrophotographic imaging members of the types abovedescribed.

Other objects and advantages of the invention will be apparent from thefollowing description and the ap pended claims.

In one form, the electrophotographic imaging member of the presentinvention is a self-supporting flexible sheet made up of a multiplicityof fiber members formed together, the fiber members including reactivegroups occurring naturally, or added thereto as will be describedhereinafter. Substantially uniformly dispersed throughout the sheet andpermanently associated therewith is a photo conductor material which ismaintained in substantially fixed position in the sheet by chemicalassociation with the reactive groups of the fibers. The fiberspreferably are those containing cellulose such as the fibers of woodpulp, cotton and other naturally occurring cellulose containing fibermaterials. For the purposes of description, however, reference will bemade to fibrous material available from wood.

Natural fibers, such as in wood, cotton, etc., are ordered bundles offibrils, and cellulose constitutes a major part of the fibrils. Theexact dimensions of the fibrils varies depending on the source, andwhile the precise dimensions of the fibrils are not clearly defined, itis known that they are larger than one molecule long and one moleculethick. In general, fibrils have a length to diameter ratio exceeding 5to 1, and the diameter is a small fraction of a micron. In unpurifiednative cellulose, such as that occurring in wood, lignin andpolyglucuronic acids are present, the latter having a structure similarto chemically pure cellulose but including carboxyl groups in the placeof the methyl alcohol groups of each ring of the molecular chain.

In the chemical processing or pulping of wood chips, a considerableamount of the lignin is removed, leaving cellulose and polyglucuronicacid present in the individual fiber structure. Some carboxyl containingmaterials of the fiber have been generally classified as hemicellulosematerials including polyglucuronic acid.

The processing of cellulose-containing fiber materials for themanufacture of paper usually includes the use of additives which alterthe Zeta potential of cellulose, leaving residues or contaminants in thefinished sheet which are detrimental for electrophotography. Theseadditives which res lt in the presence of mobile ionic charge carriers,broadly are characterized as materials providing ionic charge carriersor materials which solubilize other compounds to produce ionic chargecarriers. In either case they act to increase the electricalconductivity of the sheet to a point where it is no longer useful inelectrophotography. Typical such materials are low molecular weightalkali metal salts, non-volatile amines and amides, organic non-ionicmaterials which are hygroscopic, such as polar non-ionic surface activeagents including their non-volatile residues, nitrogenous materials, andalcohols. The non-ionic organic contaminants are also characterized by alow molecular weight and a high dipole moment compared to that ofcellulose.

Some of these additives adversely affect the electrophotographiccharacteristics of the sheet by ionization through interaction withwater (absorbed by the sheet from the air) to form ionic chargecarriers. These additives include, for example, acidic paper makersalum, internal sizing additives such as metallo-organic salts, andfillers such as some clays and chrysotile asbestos fiber which increasethe electrical conductivity of the sheet. While the detrimental effectof the presence of some of these materials may be overcome byeffectively reducing the water contained in the sheet, for example, to abone dry state, before carrying out the electrophotographic process, itis preferred in accordance with the present invention that the presenceof these materials be eliminated. An effective Way of removing some ofthe materials is by washing the pulp in single or multiple stages beforeintroducing the furnish on the drainage wire of the paper makingmachine. In other instances, the nature of the additive is such that itis removed only with difliculty by conventional washing procedures, andin such cases, the procedures of stock furnish preparation should besuch that the use of these additives is eliminated entirely.

In some instances, the nature of the low molecular charge carrier issuch that it is volatile, and while a portion of it may be removed bywashing, the remainder or a substantial portion of the additive may beremoved during the sheet drying operation.

Conventionally prepared stock using one or more of the additivesdescribed above was used in an attempt to form an electrophotographicimaging member in which French process zinc oxide was mixed with thestock and formed into a sheet. The zinc oxide was present in the finalsheet between 50% to 400% based on the bone dry Weight of the stock. Theresults indicated that no image could be produced, and furthermore,electrometer tests indicated that the sheet could not be printed becauseof the absence of any measurable light decay characteristic. Byextracting the pulp as described above, to remove these contaminants, achemically cleaned pulp was provided and was used to form a sheet inaccordance with the present invention by the addition of a particulatephotoconductor, for example, zinc oxide. The sheet was charged, exposedand developed and provided an image.

For example, several sheets were made using between one and three gramsof chemically cleaned wood pulp which was diluted to a consistency of0.3%. An aqueous slurry of photoconductive zinc oxide was added to theaqueous slurry of fiber while mixing. The amount of zinc oxide in theslurry was varied from between one to four parts by weight that of thefiber (bone dry weight), and the resulting mixtures were formed intohand sheets of about eight inches by eight inches with a retention ineach case of sufiicient amount of zinc oxide to provide between 50% and400% in the finished sheet. The sheets were drum dried at between 200 to230 F. for five minutes, and subsequently calendered. Before printing,the sheets were allowed to reach a relative humidity of less than about45%, and printed by charging and exposing them to an original for two tofour seconds using a 250 watt photoflood lamp. In exposing the sheets, ahigh contrast positive transparency was used and was placed in o elyspaced relation to the sheet being exposed.

Subsequently the sheets were developed with a liquid developer and aprint was observed. By varying the amount of chemically cleaned fibersfor a given sheet size, the basis weight of the paper or its weight perunit area could be varied.

The above procedure was followed using batches of thirty grams of fiberwith between 50% and 400% of photoconductive zinc oxide present in thefinished sheets based on the bone dry fiber weight, and similar resultswere observed. By increasing the amount of fiber, the basis weight ofthe sheet was increased.

Hand sheets formed as above described were made with varying percentageof air, for example, loose fiuffs containing approximately 85% air. Uponcharging, exposing and developing an image was formed. By calendering,the quality of the image, particularly image density and continuity wereimproved'by as much as five times.

The results obtained utilizing chemically cleaned pulp tended toindicate the presence of reactive groups in the wood fiber, either alongthe surface thereof or in the interior of the fiber member, and thatsuch groups cooperated to maintain the zinc oxide, or otherphotoconductor, such as titanium dioxide or zinc sulphide, substantiallypermanently chemically bound to the fiber. It is believed that the zincoxide particles deposit on or form an array along the outer surface ofeach of the fibers of the pulp mass as controlled by the distribution ofcarboxyl reactive groups along the length of the fiber. As a sheet isformed, the matting and intertwining of the fibers into a network formsa self-supporting structure.

The fibers used to prepare the sheets in the above identified exampleswere approximately 2,500 to 5,000 microns long and approximately to 30microns in diameter while the particulate photoconductor varies fromabout 0.2 to about 0.4 micron in diameter.

A significant feature of the present invention is to increase thecontent of the reactive groups of the fiber over that occurringnaturally to increase the retention of photoconductor in the finishedsheet. One method of increasing the amount of reactive groups in thefiber was to bleach the chemically pure pulp, the bleaching operationincreasing the carboxyl content by oxidation. The pulp was thereafterwashed to remove residual bleach and other contaminants, and formed intoimaging members.

Another method utilized to increase the reactive groups on the fiberswas to disperse the pulp in an aqueous medium, and add ferrous ions tothe aqueous slurry so that the ferrous ions entered into an ion exchangereaction with the carboxyl groups. Thereafter, a carboxyl containingethylenically unsaturated monomer such as acrylic acid was added to themixture along with hydrogen peroxide catalyst so that the monomer waschemically reacted to the fiber near the points where the carboxyl groupof the fiber had entered into an ion exchange reaction with the ferrousion. For further information as to this process, reference is made toU.S. Patent No. 3,083,118. With this mechanism, additional carboxylgroups were added to the fiber thus increasing the retention ofparticulate photoconductive material along the length of the fiber toincrease the quality of the electrophotographic print.

Approximately 3 grams of chemically cleaned paper fiber was pretreatedas above described to polymerize methacrylic acid monomer onto the fibersuch that there was a one percent increase in the weight of the paperfiber. To an aqueous slurry of the treated fiber at a pH 7 or above (byuse of ammonia or acetic acid, as required), approximately 100 to 300percent by weight (bone dry fiber weight) of photoconductive zinc oxidewas added, and hand sheets formed as above described. Upon charging,exposing and developing using a high contrast positive transparency,images were visible. Other materials which may be used in graftingcarboxyl groups onto the fiber include alpha or beta methacrylic acid(including crotonic acid), itaconic acid, acrylic acid and maleic acid,these acids being included on the fiber either as a homopolymer or acopolymer with non-acidic vinyl monomers, and mixtures thereof. Thesematerials may be generically identified as ethylenically unsaturatedmonomeric acids including one or more carboxyl groups. Preferable acidicmaterials are also characterized by the fact that they are watersoluble.

Another procedure for increasing the carboxyl content of the fibrousfurnish includes admixture therewith of a latex of carboxylated polymerssuch as a copolymer of crotonic acid and vinyl acetate having arelatively low percentage of carboxyl groups or a carboxylatedstyrenebutadiene latex. The percentage of carboxylation of these laticesis relatively small, the carboxyl groups being utilized in the latexstructure to promote a mechanism for stabilizing the latex particlesuspension against aggregation and flocculation as opposed to the use ofsoaps or anionic or cationic dispersing agents. Thus, these particularlatex materials do not include the usual dispersing agents in quantitiessufiicient to operate as contaminants in electrophotographic techniques.

Other latex polymers which may be used include terpolymers of styrene,butadiene, and one or more ethylenically unsaturated acidic monomers,for example, acrylic acid, fumaric acid, or crotoni-c acid. The styrenecontent of the polymer is at least 30% while the acidic monomer contentis between 1% to 10%, the latex particle size being between 700 and50000 Angstrom units. The terpolymer possesses a glass transitiontemperature of less than C. and preferably in the range of 25 to 35 C.,and possesses a viscosity average molecular weight exceeding 200,000.For the purpose of the present invention, carboxylated latex materialshaving a glass transition temperature as described above may be used toincrease the carboxyl content of the fibrous material.

A series of sheets were made by diluting three grams of paper fiber to0.3% solids consistency with water. The latex of the type previouslydescribed was added dropwise with agitation while the dispersion wasmaintained at a pH of about 7. Latex was added in varying amounts ofbetween 1% to 25% solids weight based on bone dry fiber weight. Anaqueous slurry of zinc oxide was added while the mixture was agitated.The amount of zinc oxide being added was varied from 3 to 12 grams. Theresultant aqueous slurries of latex, fiber and zinc oxide were placedinto the headbox of a hand sheet forming machine and sheets formed ofapproximately 8 inches by 8 inches in size. The resultant sheets weredrum dried at between 200 and 230 F. for about five minutes and thencalendered. After calendering the sheets in some cases were printedimmediately and in other cases Were allowed to come to an equilibriumcondition in an atmosphere of less than about 50% relative humidity andthen printed.

The use of a latex operates to increase the dry and wet strength of thefinished sheet while retaining an increased quantity of zinc oxide, andto this end, the latex is preferably of uniform size having a particlesize less than about 1000 Angstrom units and an average particle size ofapproximately 750 Angstrom units. This smallness of size in the latex isdesirable because the latex appears to plate out on the fiber, adheresthereto by chemical cohesive forces, e.g. secondary valence forces, andhelps the fiber to pick up zinc oxide more efiiciently. It is believedthat the latex, being attracted to the fiber, comes close to those areaswhich are active carboxyl sites. It is desirable that the latex bepresent in an amount not greater than about 25 by weight (bone dryweight of paper fiber), and it has been observed that when present in anamount of approximately l%, the latex operates satisfactorily.

In another form of the present invention, wood fiber which has had thecarboxyl content increased by a polymer deposition procedure previouslydescribed may be used as a starting material to which a carboxylatedlatex is added, using the procedures generally described previously. Byvarying the percentage of carboxyl content by polymer deposition throughpolymerization, or addition of a carboxylated latex, thehydrophobic-hydrophilic balance of the fibrous material may be varied.For example, a sheet to which latex has been added and wherein thecarboxyl content of the fiber has been increased is more hydrophobicthan one in which the latex has been omitted. A sheet including acarboxylated latex exhibits increased wet strength properties because ofthe increased hydrophobic nature of the sheet.

Other modifications and procedures which have been used include theaddition of small amounts of ammonium lignin sulfonate, or a mixture ofammonium lignosulfonate plus wood sugars commercially available underthe trademark Orzan. Approximately 0.01% by weight (bone dry fiberweight) aids in forming the aqueous slurry of zinc oxide and at the sametime helps to increase the ability of the sheet to retain anelectrostatic charge.

In chemically carboxylating the fiber it is preferred that a substantialportion of the fibers be carboxylated so that the increase of fiberweight due to carboxyl groups is less than 10% although the total weightincrease of the fiber may be as high as 300% because most of the totalweight gain is contributed by the non-carboxyl components of thecarboxylated macromolecules associated with the fiber. While the totalweight gain may be increased by 400% or more, increases above 100%reduce the ability of the modified fibers to form a strong sheet at alow temperature. Non-woven fabric techniques, using a supplementaryadhesive, tacky at low temperatures, or use of high temperatures tomelt-flow the carboxyl containing fiber adduct may be used to form asheet from fibers which have been carboxylated to a level of 0.1 to 10%by weight but with a total weight gain in excess of 100%.

A significant practical advantage of the present invention is that thinsheets having a low basis weight can be formed into satisfactoryelectrophotographic sheets. However, it is to be noted that thick sheetsof low basis weights, that is, sheets of low density are possible inaccordance with the present invention and may be printedelectrophotographically to provide good images. Thick sheets have thedisadvantages that they tend to hold a residual charge and to dischargesomewhat heterogenously rather than homogeneously.

Other additives which may be used include inorganic titanium gels ornon-photoconductive gels, optical pigments for changing the color of thesheet construction, and sensitizers customarily used withphotoconductors to extend the spectral response thereof or increasesensitivity thereof.

In the formation of the sheet and during the handling of the paperstock, it was observed that the use of relatively low pH range, forexample, in the range of 3.5 to 4.5 resulted in sheets which gave poorquality prints, and accordingly it is desired that the pH be kept nearneutral or slightly basic during processing of the chemically clean pulpand formation of the sheet. The preferred range of photoconductor isbetween 0.5 and 5 times the bone dry weight of the fiber. In the case offibers whose carboxyl content has been increased by chemical reaction oradmixture, increased amounts of photoconductor above 5 times the bonedry weight of the fiber may be used.

Bleached kraft pulp appears to give better results than bleached sulfitepulp. Further, pulp having a low Canadian freeness appears to give aslightly better image than pulp having a relatively high Canadianfreeness.

In accordance with the present invention the furnish containing thephotoconductor as previously described may be associated with a memberproviding conductivity, for example wet laminated onto a layer ofpartially dewatered paper base stock of another type, previouslydeposited onto a drainage wire as from a separate headbox. For example,any of the previously described photoconductive paper stocks may beutilized as a top portion of a sheet while the underlying portion of thesheet is formed of paper stock which may consist of between one to twograms of paper fiber and electrically conductive pigment such as aconductive non-photoconductive zinc oxide present in an amount ofbetween to 300% based on oven dry fiber weight. Alternate underlyingconductive paper stocks includes those made in the proportions of one totwo grams of paper fiber to which has been added between 0.1 to 0.3grams chrysotile asbestos fiber, or, one to two grams of paper stock towhich has been added two to twenty percent based on oven dry paper fiberweight of an alkylketene dimer available under the trademark Aquapel. Inthis manner a sheet may be provided which has both anelectrophotographic portion and an electrically conductive portion forfacilitating the formation and development of images. It is also withinthe scope of this invention to treat the fibers of such base stock inaccordance with any of the procedures of the invention outlined above sothe reactive groups are provided thereon, and the conductive pigment ischemically associated with the fibers. Mobile ionic charge carriers maybe substantially eliminated as noted previously if their presenceinterferes with the photoconductive portion of the sheet.

It is also possible in accordance with the present invention to wetlaminate both sides of the base stock with photoconductive paper of thetype previously described. In this case, the paper base includes paperfiber and asbestos fiber, supra, or alkylketene dimer with a highconductivity zinc oxide or combinations thereof, with each surface ofthe paper base member having wet laminated thereon and integrallyassociated therewith a photoconductive paper of the type previouslydescribed.

The advantages of the improved photoconductive imaging member of thepresent invention includes the fact that there is no continuous binderphase as is utilized in the conventional imaging members whichincorporate a particulate photoconductor. This substantially reducescurl problems due to changes in relative humidity and/ or combinationsof relative humidity and temperature because of the fact that the sheetconstruction in accordance with the present invention is symmetrical.Additionally, the imaging member of the present invention may be handledmuch in the same manner as an uncoated paper sheet in that basis weight,burst, and tear strength and various other characteristics may be variedto produce varying physical characteristics in the sheet depending onthe desired use thereof. For example, the sheet may be made as thin astissue paper or as thick as blotter paper and is still printableelectrophotographically. Further, the sheet is printable on each side,that is a latent image may be formed on one side and developed whilepreventing deposition of developer on the other side. After formation ofthe first image, the sheet or web may be printed on the reverse side,with the same precaution being taken to prevent developing thepreviously printed side of the sheet.

Since additives may be included in the sheet, particularly resinous typematerials and preferably carboxylated materials such as the laticespreviously mentioned, the sheet may be formulated to providesubstantially wet strength characteristics thereby permitting formationof a sheet which maintains its physical integrity when in contact withan aqueous medium.

In accordance with the present invention, the photoconductive pigment ispresent in an amount sufficient to provide a stable electrostatic latentimage upon exposure of a charged image member to a light pattern. It hasbeen observed in accordance with the present invention that the ratio ofzinc oxide to fiber may be as low as 0.5 :1 and the paper will operatesatisfactorily to produce an image electrophotographically. This issignificantly less than the ratio of photo conductor to resinousadhesive binders used in conventional coated electrophotographic imagingmembers. The result is that in the case of pigments such asphotoconductive titanium dioxide, zinc oxide, zinc sulfide or mixturesthereof and the like, a reduced amount of such pigments distributedthrough the sheet likewise reduces substantially the abrasive characterof the sheet. Also, the overall weight of the sheet is far less than theweight of a corresponding imaging member in which the photoconductor isuniformly dispersed in a continuous binder as a coating on paper orother substrates.

While the article and method herein described constitutes a preferredembodiment of the invention, it is to be understood that this inventionis not limited to this precise article and method and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. An electrophotographic imaging member comprising a surface portioncontaining intertwined and matted fibrous cellulosic material and afinely divided metal ion containing photoconductor material dispersed insaid fibrous material, said fibrous material being substantially free ofmobile ionic charge carriers for providing said surface portion with ahigh electrical resistance in the dark for holding an electrostaticcharge applied thereto, said fibrous material having carboxyl groupschemically associated therewith, said photoconductor being substantiallypermanently chemically associated with said carboxyl groups, and saidchemically associated photoconductor material being present in saidsurface portion in an amount suflicient to permit formation of anelectrostatic latent image thereon upon exposure to a light pattern.

2. An electrophotographic imaging member as set forth in claim 1 whereinsaid fibrous material contains cellulose fibers in major proportion.

3. An electrophotographic imaging member as set forth in claim 1 whereinsaid photoconductor is present in an amount between 0.5 and 5 times thedry weight of said fibrous material.

4. An electrophotographic imaging member as set forth in claim 1 whereinsaid matted fibrous material includes a carboxylated latex polymer.

5. An electrophotographic imaging member comprising a self-supportingand flexible sheet of intertwined and matted fibrous material, saidfibrous material being a naturally occurring wood fiber modified, whilepreserving its fibrous form, to have a reactive carboxyl group contentgreater than that naturally occurring in said wood fiber, a finelydivided metal ion containing photoconductor material admixed with saidfibrous material, said fibrous material being substantially free ofmobile ionic charge carriers for providing said sheet with a highelectrical resistance in the dark for holding an electrostatic chargeapplied to a surface thereof, said reactive carboxyl groups chemicallyassociated said photoconductor to said fibrous material, and saidphotoconductor material being present in an amount suflicient to permitformation of an electrostatic latent image thereon upon exposure to alight pattern.

6. An electrophotographic imaging member including a conductive baseportion and at least one surface portion, said surface portioncomprising a layer containing intertwined and matted fibrous cellulosicmaterial, said fibrous material including carboxyl groups, a finelydivided metal ion containing photoconductor material being substantiallypermanently chemically associated with said carboxyl groups, said mattedfibrous material being substantially free of mobile ionic chargecarriers for providing said surface portion with a high electricalresistance in the absence of light for holding an electrostatic chargeapplied thereto, and said photoconductor material being present in anamount suflicient to permit formation of 10 an electrostatic latentimage on said surface upon exposure to a light pattern.

7. An electrophotographic imaging member according to claim 6 whereinthe conductive base portion comprises intertwined and matted fibrouscellulosic material having carboxyl groups chemically associatedtherewith and a finely divided electrically conductive pigmentchemically associated with said carboxyl groups.

8. An electrophotographic imaging member according to claim 6 andincluding a further surface portion on the opposite side of said baseportion to provide an imaging member having photoconductive surfaceportions on opposite sides of said conductive base portion.

9. An electrophotographic imaging member comprising a self-supportingflexible sheet including a surface containing intertwined and mattedchemically modified fibrous cellulosic material, said modified materialcontaining reactive carboxyl groups and being the polymeriz'ationreaction product of a fibrous cellulosic material and a carboxylcontaining monomer and having a high electrical resistance in theabsence of light, said carboxyl containing monomer being present byweight in an amount not greater than 10% based on the dry weight of saidfibrous material, and a metal ion containing photoconductor pigmentchemically associated with said modified fibrous material in an amountsufficient to permit formation of an electrostatic latent image on saidsurface upon exposure to a light pattern.

10. An electrophotographic imaging member as set forth in claim 9wherein said fibrous material is cellulose.

11. An electrophotographic imaging member asset forth in claim 9 whereinsaid member includes between 1% and 25% by weight of said fibrousmaterial of a carboxyl containing latex polymer having a glasstransition temperature less than about C.

12. An electrophotographic imaging member as set forth in claim 9wherein said fibrous material is the reaction product of naturallyoccurring wood fiber and at least one organic carboxyl containingmonomer.

13. An electrophotographic imaging member as set forth in claim 12wherein said member is free of mobile ionic charge carriers.

14. An electrophotographic imaging member as set forth in claim 11wherein said photoconductor is zinc oxide.

15. An electrophotographic imaging member as set forth in claim 14wherein said zinc oxide is present in a ratio by weight of from 1:05 to1:5 of fibrous material to photoconductor.

16. An electrophotographic imaging member as set forth in claim 11wherein said carboxyl containing latex polymer has a particle size inthe range of 700 A. to 5,000 A.

17. The method of producing an electrophotographic imaging membercomprising the steps of providing a material containing fibrouscellulose having reactive carboxyl groups thereon, said fibrous materialbeing free of mobile ionic charge carriers and capable of forming aself-supporting flexible sheet, admixing an aqueous slurry of saidfibrous material with a finely divided metal ion containingphotoconductor capable of chemically associating with said carboxylgroups, and dewatering said mixture of photoconductor and fiber to forma sheet including a surface portion having a high electrical resistancein the absence of light and having a sufiicient amount of saidphotoconductor to form an electrostatic latent image upon exposure to alight pattern.

18. The method as set forth in claim 17 wherein said fibrous materialcomprises in major proportion cellulose fibers and wherein said mobileionic charge carriers are removed by washing.

19. The method as set forth in claim 17 wherein said fibrous material isa naturally occurring cellulose material, and wherein said fibrousmaterial is reacted with an organic carboXylic acid to increase theactive carboxyl groups on said fiber above the amount occurring natural-20. The method as set forth in claim 17 including the step of adding tosaid slurry sufficient carboxyl containing latex polymer to providebetween 1% and 25% by dry weight of said fibrous material of said latexpolymer prior to the addition of the photoconductor.

21. The method as set forth in claim 19 wherein said organic carboxylicacid is a carboxyl containing ethylenically unsaturated monomer, andwherein said monomer increases the dry weight of fiber not more than10%.

22. The method as set forth in claim 17 including the step ofcalendering the sheet after formation thereof.

23. The method as set forth in claim 21 including the step of adding tothe slurry sufiicient carboxyl containing latex polymer to providebetween 1% and 25% by dry weight of said fibrous material of said latexpolymer prior to the addition of the photoconductor.

References Cited UNITED STATES PATENTS G'EORG'E F. LESMES, PrimaryExaminer M, B. WlTTENBERG, Assistant Examiner US. Cl. X.R.

